Answers : (2)

Sachin Tyagi

31
Points

The molecular formula of gaseous hydrocarbons can be determined even without knowing their percentage composition. A known volume of hydrocarbon is taken in eudiometer tube and exploded with an excess of known volume of oxygen. The carbon and hydrogen of the hydrocarbon are oxidized to carbon dioxide and water respectively according to the following general reaction.

After explosion, the tube is allowed to cool to room temperature. The volume of the gaseous mixture is recorded. The volume corresponds to unreacted oxygen and carbon dioxide. The volume of carbon dioxide is determined by the decrease in volume of the gaseous mixture when caustic potash solution is introduced into the eudiometer tube. The caustic potash solution absorbs whole of carbon dioxide. The gas left behind is the unreacted oxygen. Volume of oxygen used is then calculated by subtracting the volume of unreacted oxygen from the total volume of the oxygen taken initially.

The molecular formula of the hydrocarbon can be evaluated by knowing

(i) the volume of gaseous hydrocarbon taken.

(ii) the volume of oxygen used.

(iii) the volume of carbon dioxide produced.

There are many differences between.

1) Tautomers are definite compounds and can be separated and characterized by suitable methods, but resonating structure cannot be separated as they are imaginary structure of the same compound.

2) Tautomerism involved the migration of a mobile hydrogen atom between two polyvalent atoms present in the molecule and thus tautomers differ a change in the position of atoms. On the other hand, resonating structures have identical atomic arrangement and involves only a change in the position of pi-electrons or unshared electrons.

3) Tautomers are in dynamic equilibrium with each other and interconvertible but no such equilibrium exits in resonance and there is only form which is intermediate between the many contributing structures.

4) Two tautomers have different functional groups, but the various resonating structures have same functional group.

5) Tautomerism has no effect on bond length, while resonance is accompanied by an increase in bond length of a double bond and decrease of a single bond length.

6) Tautomerism has no contribution in stabilizing the molecule and does not lower its energy, but resonance lowers the internal energy and thus gives rise to extra stability to a molecule.

7) Tautomerism may occur in planar or nonplanar molecules, while resonatrice occurs only in planar molecules.